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No, it’s not what you think. In fact, the aerodynamic object above isn’t even organic, let alone avian. Bearing a resemblance to bird wings, it’s a hunk of hematite, a mineral formed from iron and oxygen. Photographer Rosamond Purcell shot this specimen for A Glorious Enterprise, a 464-page tome commemorating the bicentennial of the Academy of Natural Sciences in Philadelphia, America’s oldest natural history museum.

Aptly christened “Bird Wing” by museum curators, this chunk of hematite represents one of about 466 mineral specimens collected by William Sansom Vaux (his namesakes include the Vaux’s swift). A Quaker and lawyer by training, Vaux was also a passionate mineralogist, particularly drawn to aesthetically appealing specimens—especially hematite. He procured this shimmery, dusty-rose piece from the English Midlands, once a hotbed for quarrying. Upon his death in 1882, Vaux left a 6,000-piece mineral collection to the Academy.

Purcell was a natural fit to shoot selections from the museum’s rich stash, having collaborated with multiple natural history institutions, including Harvard’s Museum of Comparative Zoology, where she worked with paleontologist Stephen Jay Gould. “I must be a sucker because I think that one thing is amazing after another,” she says. “I can just spend a whole day driving a curator crazy wanting to see the next [item].” Purcell staged several pictures on the Academy’s roof, where natural light and various topographic textures provided a perfect setting. “She is just the most amazing person in her ability to take objects and see them in new and interesting ways and breathe life into them with her own magic,” says curator Robert McCracken Peck, who, with Patricia Tyson Stroud, wrote A Glorious Enterprise.

The hematite’s uncanny resemblance to avian anatomy charmed Purcell. “I’m very keen on something that is something but looks like something else,” she says. The mineral’s structure is even birdlike—it’s thick at the base and thinner as it fans out, “just the way a wing would be.” Although the specimen isn’t on display at the Academy, the public can view it this October at the Folger Shakespeare Library in Washington, D.C., where it will be on exhibit with other earth-born items resembling artwork that Purcell has assembled. “It’s just a beautiful object,” she says.